1. Field of the Invention
The present invention relates to a linear motion rolling guide unit that linearly guides a movable element to be moved in a linear movement mechanism such as a machine tool or industrial robot, and a vibration isolation apparatus that gives vibration isolation properties to said unit.
2. Description of the Prior Art
An example of this type of linear motion rolling guide unit of the prior art is disclosed in, for example, Japanese Patent laid-open No. 2-279243, and its constitution is indicated in FIGS. 1 through 3.
As indicated in FIG. 1 and FIG. 2, this linear motion rolling guide unit has a track rail 3 fixed on a frame in the form of machine tool bed 1 by bolt 2 (shown in FIG. 2), and two sliders in the form of sliding units 5 of the first type guided by said track rail 3. A sliding unit of the second type in the form of vibration isolation unit 6 is equipped sandwiched in between each of these sliding units 5, which is also guided by track rail 3 as is clear from FIG. 3. Rectangular plate-shaped table 8 is mounted on these sliding units 5 and vibration isolation unit 6 by bolts 9 (shown in FIG. 2 and FIG. 3).
As indicated in FIG. 2, a total of four track surfaces 3a, for example two surfaces each on the right and left sides, are formed in parallel along the axial direction in track rail 3. Both sliding units 5 are straddled across track rail 3, and a portion of said sliding units 5 have four circulating paths 5a in opposition to these track surfaces 3a corresponding to each track surface. A plurality of rollers 10 are arranged and contained within each of these circulating paths 5a functioning as rolling elements that bear the load between track rail 3 and sliding unit 5 by circulating while rolling over track surfaces 3a accompanying movement of sliding units 5.
On the other hand, as is clear from FIG. 3, vibration isolation unit 6, provided as a damper, is also straddled across track rail 3, and a narrow cushioning gap 13 is provided between said vibration isolation unit and track rail 3. An oil film is formed in this cushioning gap 13 by oil being supplied through hole 6a provided in vibration isolation unit 6.
Two sets of the above-mentioned linear motion rolling guide unit (only 1 set of the linear motion rolling guide unit is shown in FIG. 1) are provided in parallel on the bed indicated in FIG. 1, and both support table 8. In this constitution, a workpiece (not shown) is placed and held in position on table 8. Table 8 then moves back and forth in the direction indicated by arrow F by a driving device not shown to allow the required processing for said workpiece, such as cutting work, to be performed.
In the linear motion rolling guide unit of the abovementioned constitution, during the time cutting work on the workpiece is being performed, said linear motion rolling guide unit is subjected to mechanical vibrations. When measures have not been implemented to isolation such vibrations, the problem occurs in which the processed surface becomes heterogeneous due to the presence of such vibrations. Therefore, by charging oil into cushioning gap 13 formed between track rail 3 and vibration isolation unit 6 as described above in the prior art, vibrations between said track rail 3 and vibration isolation unit 6 are cushioned thus improving the finished accuracy of the processed surface.
However, although the prior art can be expected to demonstrate damping effects only when oil is uniformly filled into the cushioning gap as described above, since the surface tension of oil filled into cushioning gap 13 weakens due to the effects of vibrations or decreases in viscosity caused by heat and the passage of time, and the oil gradually runs down from track rail 3, in order for damping effects resulting from this oil film to continue to be maintained, oil must be supplied frequently, thus resulting in the disadvantage of bothersome maintenance. In addition, the prior art also has the problem of it not always being easy to form this cushioning gap to a uniform size over the entire range of the area at which it is to be provided.